The invention relates to a device for generating blue laser light having a wavelength of 445 to 455 nm by means of an upconversion process, said device including a pumping laser and a resonator cavity comprising a fluoride-containing material having trivalent thulium ions.
The invention further relates to a method of generating blue laser light by means of an upconversion process using a pumping laser and a resonator cavity which comprises a fluoride-containing material having trivalent thulium ions.
The device in accordance with the invention may be used, for example, as a compact light source for optical storage of information and for telecommunication. By using light of a short wavelength, the information density can be increased and the possibilities of writing and erasing information are enlarged by virtue of the larger photon energy.
In an article by D.C. Nguyen et. al. in Applied Optics 28 (17), pages 3553 to 3555 (1989), an upconversion process and a device for carrying out such a process are described, a single crystal of yttrium lithium fluoride doped with 1 at % of trivalent thulium ions being used in the process. The crystal is irradiated by two laser-light sources having wavelengths of approximately 781 nm and 649 nm. Coherent blue laser light having a wavelength of approximately 450 nm is generated. Said light is generated in the form of pulses.
A disadvantage of the known device is that pulsed laser action is unsuitable for use in equipment for the optical recording of information. A further disadvantage is that the use of two (different) laser light sources leads to a complicated construction and a device which is far from compact.
A problem in the manufacture of said known device is the necessity of providing a large absorption length of semiconductor laser light, which is difficult to realise in a crystal. This is necessary because the concentration of thulium ions must be comparatively low (less than approximately 1 mol %), since excited thulium ions easily give rise to efficient cross-relaxation processes which substantially reduce the effectiveness of the upconversion process.